Vacuum operated servomotor



Sept, 19, 1944. s. E. wlLLETT ETAL VACUUM OPERATED SERVO-MOTOR Filed May18, 1942 4 Sheets-Sheet 1 zENTORs ATTGRNEYS um N Sept 19, 1944 s. E.wlLLETT ET AL VACUUM OPERATED SERVO-MOTOR Filed May 18, 1942 4Sheets-Sheet 2 Sept 19 1944- s. E. wlLLETT ETAL 2,358,753

VACUUM OPERATED SERVO-MOTOR Filed May 18, 1942 4 Sheets-Sheet I5 w uw @smi w Nw n. u ww @W M L ATTOQNEYS Sept 19, 1944. s. E. WILLETT ET AL2,358,753

VACUUM OPERATED SERVO-MOTOR Filed May 18, 1942 4 Sheets-Sheet 4 "a."IIIIIL';

www? B7 QM* ATTORNEYS Patented Sept. 19, 1944 VACUUM OPERATED SERVOMOTOBSydney Edgar Willett and Stanley Howard Edge,

Lincoln, England, assignors to Clayton Dewandre Company Limited,Lincoln, Enxland Application May 1s, 1942, serial No. 443,526 In GreatBritain May 30, 1941 17 Claims.

This invention relates to vacuum or pressurev operated servo brakedevices and to the kind wherein the movements imparted to a hand leveror pedal are transmitted through reaction mechanism having connectionsto a control valve and a servo cylinder whereby the movement of a pistonin the cylinder is utilised to augment the effort transmitted to anoutput shaft or rod which is connected directly to the brake applyingmeans.

Vacuum operated servo devices for application to automobile roadvehicles are commonly constructed as units, the casing of each unitembodying a vacuum cylinder, a valve (hereinafter referred to as thedistributor valve) controlling the admission of air or vacuum to thecylinder and an arrangement of levers for transmitting manual eifort tothe valve and for enabling the movement of a piston in the cylinder toreact upon the transmitting means. As vehicles tted with these units,especially vehicles used in warfare, frequently have to traverse countrywhich may be sandy or waterlogged it is essential, in order to ensureefficient operation of the servo unit, that its component parts shall beadequate- 1y protected against the ingress of sand, mud and water whilstpermitting entry of a sulcient amount of air when required to releasethe vacuum in the operating cylinder.

The object of the present invention is to provide improvements in suchbrake operating units,

proved servo brake device are all constructed as a unit wherein the airinlet is to the said casing in which the air is caused to take atortuous path and to pass over a baille or -baiiies for the purpose ofremoving its dustcontent before it enters a passage or conduit leadingto the distributor valve.

The invention also includes improved distributor valve arrangements andpiston constructions all designed particularly for application to thesaid servo brake unit for the purpose of rendering the same compact,light, dust free and positively lubricated.

Reference will now be made to the accompanying drawings which illustratea construction according tothe invention and in which:

Fig. l is a sectional elevation of a complete monobloc servo brakeoperating unit.

Fig. 2 is a cross-sectional elevation taken on the line A-A of Fig. 1.

Fig. 3 is a diagrammatic perspective view ofl such improvements beingdesigned more partic- A ularly for application to heavy transportvehicles or armoured vehicles to enable the braking eifort applied to bedirectly transmitted to the operating components, to protect theoperative parts of the unit against the ingress of sand, mud and waterwhilst permitting entry of a sufficient amount of air for operativepurposes and also to improve the construction and arrangement ofcomponent valves and pistons to facilitate assembly and .ensure emciencyin operation.

According to the invention a monobloc servo brake unit of the kind abovedescribed is pro and 2,

Fig. 4 is a detail view of an air inlet to the casins,

Fig. 5 is a sectional elevation of a valve construction applicable tothe unit shown in Fig. l,

Fig. 6 is a sectional elevation of an alternative valve construction,

Fig. 7 is a sectional elevation of an alternative piston constructionfor use in the servo cylinder, and

Fig. 8 is a vertical section and Fig. 9 is an exterior elevation of thelower portion ofthe casing of the device, showing on an enlarged scale avalve for the relief of excess air pressure or oil.

In the construction illustrated and referring first to Fig. 1, themonobloc servo unit comprises a main casing i which is formed integralwith a servo cylinder 2 and is attached to a valve housing 3.

The brake control is initiated by means of a pedal actuated rod 4 whichpasses through a flexible boot 5 into the casing i. The function of theboot 5 is to prevent ingress of dust, mud or water as the rod 4 isreciprocated. l The rod 4 terminates in an eye 6 surrounding a tubularbushing 1 carried by two arms 8 and 8a which together form the reactionlever of the mechanism. The bushing 1 surrounds, but is spaced from, apin 9 whose outer portions pass through a pair of brake levers I0 andIlla, the outer ends of said pin 9 having ailixed thereto the forkedends ii of an output rod i2 which is connected to the brake applyingmechanism. The brake levers I and Illa are movably mounted at theirupper ends around a fixed pivot rod I3 whose ends are mounted in theside walls of the casing I as shown in Fig. 2. The brake levers I0 andIlla are pivotally connected to the arms 8 and 8a by means of a pin I4and the upper ends of the arms 8 and 8a carry a bushing I5 which freelysurrounds and is spaced from the pivot rod I3, the said bushing alsocarrying an eye I6 formed at one end of a. bolt I1 connected to apivoted lever I8 through which the rod I3 of a distributor valve housedin the casing 3 is operated. The arrangement above described will bemore readily understood by reference to the perspective diagram, Fig. 3,wherein, for the sake of clearness, the various arms and levers areshown more widely spaced along the rod I3 than they are in actualpractice.

The lower end of the reaction lever 8 is connected by an arm to a piston2l in servo cylinder 2 the said piston being adapted to make itsoperative stroke against the resistance oi' a spring22. A spring 23opposes movement of the reaction lever towards the position shown inbroken lines in Fig. 1, and assists in restoring it to its inoperativeposition when pressure on the operating pedal is relaxed. The ends ofspring 23 are enclosed in the wall of casing I at 24 (Fig. 2).

An air inlet to the casing I isshown at 25, Fig. 1 and may be simply acowled inlet or may communicate by means of a conduit indicated bybroken lines 26 with an inlet situated at a higher level than theuppermost part of the casing I. The casing is otherwise sealed againstentry of air as the output spindle I2 is also litted with a flexibleboot 21. The only other opening in the casing is at 28, this openingbeing normally closed by a valve capable of opening when the level ofoil within the casing exceeds a predetermined amount. This valveconsists of a flexible ldap 28 xed to the outer side of the casing byscrews 28, the tlap having two vertical slits 28h so that its centralportion 28 is free at its lower portion and can swing open to uncoverthe opening 28 in the lower portion of the casing, as shown in detail inFigs. 8 and 9, and thereby permit escape of excess air pressure or oil.Thus, the casing is supplied with air only through the inlet and whenthe distributor valve 3 is moved to a position in which the vacuum incylinder 2 is relaxed, air for this purpose is supplied only from withinthe casing I. The position of the air inlet 25 and the presence of thesystem of levers 8, 8a, I0 and Ina. between this inlet and the inlet 23to the distributor valve causes the air to take a tortuous path and indoing so to deposit its dust content, this operation being aided by theprovision of a baille 33 adjacent the inlet 29 over which baille the airis compelled to pass to reach the inlet. By forming this baille with aninclination as shown or by the addition of a lip 3I, a surface is formedagainst which the air strikes and which causes deposit of dust bychanging the direction of motion of the air. It will be understood thatthe nature and position of the air inlet 25 will prevent ingress of anyrelatively large particles of solid matter and that the arrangementabove described for controlling the passage of air through the casing Iwill remove the iine particles of dust carried in suspense in the airwhich will deposit upon the oil in the base of the casmanana ing andeventually pass away as the excess oil escapes gradually through theoutlet 28. In this manner the mechanism of thevservo device is protectedagainst the ingress of dust which would tend to choke the tine orificesof the distributor valve mechanism and in a short time render the deviceas a whole ineffective.

In order to prevent, as far as possible, dust laden air from enteringthe casing I, the device shown in Fig. 4 may be employed. This devicecomprises a metal plug 32 externally screw threaded at 33 to enable itto be ilxed in the opening 25 which is internally screw threaded for thepurpose. Within the plug is disposed a baiiiing device in the form of adisc 34 formed with a number of radially or otherwise disposed slots 35with the material partly punched out to form the slots bent to formlouvres 36. 'Ihe outer portion of the plug is screw threaded at 31 inorder that a cowl may be mounted thereon or that a coupling member 38may be attached for screwing to the plug the conduit 26 opening in anupper part of the vehicle as previously described. By employing theslotted and louvred disc 34 as described, the incoming air is compelledby the louvres to change its course and in doing so to deposit its dustcontent in the outer part of the plug. 'Ihis arrangement is particularlysuitable for vehicles which are intended for operation in dusty or sandyareas.

The arrangements already described for excluding dust from the casing Iwill exclude water also. Servo devices of this character must ofnecessity be arranged on the underframe of a vehicle, and if thatvehicle is destined for use in rough country where streams have to becrossed, the conduit 28 is essential so that the actual air inlet issituated above the level of any water through which the vehicle mustpass. Pressure of water upon the exterior of the casing I would tend toclose the valve controlling the opening 23 (not shown) firmly onto itsseat so that no water would enter the casing through the opening 28.This arrangement of an inlet control has been designed so as to vary aslittle as possible the usual manner oi.' manufacture of servo brakeoperating units and also to avoid any substantial addition to the costthereof.

The valve operating rod I9 is secured to a stirrup 39 (Fig. 5) which isadapted to engage a collar 40 at one end of a valve spindle 4I whichcarries valve members 42 and 43, the valve member 42 being looselymounted on the spindle and the valve member 43 being xed to the spindle.The two valve members are movable in the cylindrical housing 3 havingports 44 and 45 adapted to communicate with the servo cylinder 2 throughspace 48 and port 41 in the wall of said cylinder. The end of the valvehousing 3 remote from the rod I3 is connected to a conduit 48communicating with a source of vacuum and this end of the housing isnormally closed by a valve disc 49 of yleldable material which iscarried by the valve member 43 and seats on an annular seating 50 onwhich it is held by the action of a spring 5I disposed in an annularspace 52 between the two valve mem bers 42 and 43. The valve member 42also carries a valve disc 53 of yleldable material which is adapted toseat on an annular seating 54 but is normally held oil! its seating bymeans of a sleeve 55 slidable on the spindle 4I one end of which sleeveabuts against the inner end o1' the stirrup 39 so that under normalconditions air which enters the casing 3 through the -annular passage 29surrounding the rod i9 'can pass through an annular passage 59surrounding the sleeve yIl and pass through the port 44, space 49 andport 41 into the servo cylinder 2. When the rod I9 is moved towards theleft (Fig. 5) by the pedal operated mechanism the pressure of thestirrup 39 on the sleeve 55 is relaxed so that the spring 9i can expandand push the valve member 53 on to its seating 54 and thereby shut offthe air supply to the cylinder 2.' This movement of the rod I9 alsocauses the stirrup 39 to exert 'a pull on the collar 49 to move thcspindle 4I towards the left to pull the valve disc 49 off its seatingand thereby open the cylinder 2 to vacuum through the port 45, space 49and cylinder port 41. Immediately the pull on the rod I9 is relaxed thespring 5i restores the valve disc 49 on to its seating to shut off thecylinder from the vacuum and the sleeve 55 operates, as alreadydescribed to open the air inlet port 44.

The construction illustrated in Fig. 61s designed for use where greatercompactness is required than in Fig. 5. Similar reference numerals areused to indicate parts similar to those shown in Fig. 5, but the twoconstructions diifer essentially in that in Fig. 6 a valve member 51 isdisposed slidably within a valve member 5o which carries the yieldabledisc 49 adapted to engage the seating 59 to shut 0E the cylinder 2 froma vacuum conduit secured to the socket 49. The valve members arenormally held apart on their seatings by a spring 59 and the valvemember 59 is secured to the spindle 4i carrying the collar 49 with whichthe stirrup 39 is adapted to engage as in the previous construction.

The valve member 51 carries the yieldable valve disc 53 and has acylindrical extension 99 over which a sleeve 9i is mounted, this sleevebeing engaged by the end of the stirrup 39.

With the construction shown a pull exerted on the stirrup towards theright (Fig. 6) will move the vacuum valve disc 99 off its seatingagainst the action of spring 59, whilst movement of the stirrup in theopposite direction will push the valve member 51 towards the left andlift the disc 53 oil its seating thereby opening the interior of thecylinder 2 to atmosphere.

The valve housing 3 is sealed against entry of water by means of apacking of felt or other material 62 disposed in an annular groovesurrounding a sleeve 93 fitted within theend of the housing whichsurrounds the sleeve 5l, said sleeve 93 forming at its inner end theseating 54 for` the valve disc 53.

In operation, the opening of valve 49 allows vacuum to be exertedthrough a port 45, a space 45 and port 41 in the wall of cylinder 2.When valve 49 is closed and valve 53 is moved oil its seating, airentering through the annular passage 59 passes by way of port 44, space49 and port 41 to the cylinder 2.

In both forms of valves described the flexible valve discs 49 and 53 arepreferably formed of a synthetic rubber material such, for example, asthat known as neoprene.

The brake operating mechanism above described is provided with a pistonadapted to operate in the cylinder 2 and whose construction is such thatit is lighter than hitherto, is better adapted to resist wear and can bemore efficiently lubricated.

Referring rst to the piston shown as part of Fig. l, 94 and 95 indicatetwo steel pressings adapted to beconnected at their centres by a bolt 99to form the complete piston. The oomponent 94 consists of a plain dishedmember having a flat inner face mergedinto the side wall by a roundededge 91. The component is of frusto-conical form with a cylindricalskirt 99 and also has a ilat inner face.

Clamped between the iiat inner faces of the piston components 94 and 99is a washer 99 of flexible material whose peripheral portion 19 isforced into cup formation by insertion in the cylinder 2 with the wallof which the portion 19 is maintained in contact by an annular dishedleaf spring 1I also clamped between the components 94 and 95. between awasher 12 and the iianged head 13 of bolt 99 which head is formedintegral with an eye 14 through which passes a gudgeon pin 15 securingto said eye the end of the rod 29 through` the medium of which thelpiston movements are caused to react upon the pedal of the brakeapplying mechanism.

The nut 19 which secured the assembly above described upon the eye bolt93 also holds in position a dished washer 11 adapted to' retain inconnection with the piston one end of the spring 22 disposed within thecylinder 2 to Voppose the movement of the piston and return it to normalposition after operation.

The construction above described enables the piston components to be ofrelatively light construction consistent with strength as the actualwork of closing the end of the cylinder to ingress or egress of air asthe case may be, is performed by the washer 99 under the action of itsspring 1I. The piston assembly is thus, in effect, a framework tosupport the washer and spring and does not need to form a gas tight fitwith the cylinder walls. In these circumstances. the wear on the pistonis reduced and is a factor enabling the light structure described to beemployed.

Within the cylinder wall its outer end is a lubricant supply port 19which keeps the annular space 19 between the piston components suppliedwith lubricant whenever the piston returns to the inoperative positionshown in Fig. 1 wherein its movement under the iniluence of spring 22 isstopped by its engagement with an annular shoulder 89.

The alternative piston construction shown in Fig. '1 is designed forapplication to 'pistons of larger diameter than that shown in Fig. l andwherein a single central bolt is insufficient to hold the components incorrect operative relationship.

The piston shown in Fig. '7 consists of pressed steel components 9| and92, each component being strengthened by a central dished portion 93.The component 92 comprises two portions of differing diameters to forman annular space 94 in which operates the free portion 95 of an annularcup washer 99 clamped between the outer portions of the components 9iand 82 by a series of bolts 91 which also retain an annular leaf spring38 whose outer portion serves to maintain the portion 95 of the washerin close contact with the wall of the cylinder 2.

The central portion of the piston assembly is constructed and arrangedin a manner very similar to that already described with. reference toFig. 1 and comprises an eye-bolt 99 on which the components 9| and 92and washer 9|, retaining the end of spring 22, are clamped by means of anut 92. To the eye-bolt 99 is also connected by a gudgeon pin 93, thearm 29 connected to the brake operating mechanism.

The piston assembly is held together the bushing 1 to the The cylinder 2is provided with an oil inlet I4 which maintains a supply of lubricantto the annular space 84 at each outward or return stroke oi the pistonwhich is thereby maintained under constant and even lubricationthroughout its periods oi' operation.

'I'he casing l o1' the brake operating mechanism above described isdesigned for production by die casting and for this reason the upperportion of the said casing is closed by a sheet metal cover 85.

The general operation described is as follows:

When the operating pedal is depressed, axial movement in the directionof the arrows shown in Figs. 1 and 3 is imparted to the rod 4 and thismovement is communicated to the bushing 1, which, having directengagement with the reaction lever components 8 and 8a, causes thesecomponents to rock around the connection of their lower ends to the rod20, which they are i'ree to do owing to the lost motion connectionsbetween bushing 'l and pin 9 and between the components 8 and 8a and therod Il. 'I'he upper ends of the reaction lever components 8 and la are,therefore, rocked towards the right in Fig. l, this movement causing rodI3 to be operated to move the valve 49 (Fig. 5 or 6) oil its seat in themanner already described to place the cylinder 2 under vacuum. The pinI4, levers il, i'ork il and rod I2 advance slightly during the initialrocking of the lever components l and la, but such advance o1' theseparts may take place freely while there is slack in the brake system.'Ihe vacuum operation in the cylinder 2 subsequently move:` the wholelever system around the fixed pin I3 towards the position shown inbroken lines in Fig. 1. As the pressure applied to the pedal is relaxed,the levers rock so as to cause the valve to vent the cylinder to theatmosphere, and the spring 22 in the cylinder 2 assists the spring 23 torestore the parts to the normal positions shown in Fig. 1 in which thebrakes are om of the devices above When the vacuum supply to thecylinder is not available for any reason, the brakes can be applied bythe pedal pressure only and in that case, the effort will be appliedcentrally through pin 9 and the brake levers I0, |0a and brake operatingrod I2. This arrangement possesses the advantage that the effort appliedpasses centrally and directly to the brake operating rod I2 without anytendency to strain the transmission members by twisting and that forsuch reason the eil'ort applied to the pedal is utilised to better eiectthan in previous forms of construction.

Although the rod 4 has been described above as a push rod to apply thebrakes, it will be obvious that the invention can be equally applied toa brake applying mechanism actuated through a pull rod.

We claim:

1. A servo brake unit comprising a casing, a servo cylinder forming partof said casing, a distributor valve housing attached to said casing,transmission mechanism mounted in said casing, connections between saidmechanism and an operating pedal, brake mechanism, distributor valve anda piston in the servo cylinder, an air inlet situated in the upper partof said casing and a baille arranged to screen the air inlet to thedistributor valve housing.

2. A servo brake unit according to claim 1 wherein the said air inlet isprovided with a bafiling device having slots protected by louvres 4witha shoulder on the inner to cause deposit of dust as casing through thesaid slots.

3. A servo brake unit comprising a casing, transmission mechanism, adistributor valve and a servo cylinder mounted in said casing. areaction lever forming part of said transmission mechanism, a pedalactuated operating rod, a brake actuating rod, a common element mountedin said reaction lever to which both oi' said rods are connected, meansfor preventing ingress oi.' air to said casing around the said rods, anair inlet situated in the upper portion ot said casing. baming meanssituated adjacent said air inlet and a baille arranged to screen the airinlet to the housing of said distributor valve.

4. For use with a servo brake unit having a casing, a servo cylinderforming a part of said casing, transmission mechanism mounted in saidcasing, pedal actuating means and a brake operating rod connected tosaid transmission mechanism in such manner as to provide a directconnection from the one to the other, a lever connecting said mechanismto a piston in the servocylinder, a distributor valve housing adapted tobe secured to said casing and having an air inlet communicating with theinterior of said casing mechanism with a valve spindle movably mountedin said housing, a pair oi valve elements mounted on said spindle andadapted to control ports in said housing communicating with said servocylinder, the distributor housing having valve seats so spaced along theaxis of said spindle that when one of said valve elements is open theother is seated, and baille means for preventing entry of dust to saiddistributor valve housing air inlet.

5. A servo brake unit according to claim 4 wherein the said valveelements are movable one at a time in opposite directions according tothe direction of movement of their operating rod, a spring beingprovided which is compressed by opening movement of one valve element tomaintain the other valve element on its seat.

6. A servo brake unit according, to claim 4 wherein one of said valveelements controls a vacuum port in the servo cylinder and the othervalve element controls an air inlet port in said cylinder.

'7. A servo brake unit according to claim 4 wherein one of said valveelements is slidable within the other, the movement of the outer valvemember being limited by contact of its inner end valve member whosemovement is also limited by contact of its inner end with the closed endof the outer valve member, a spring being interposed between the twovalve members so as to be compressed by the opening of one of them tomaintain 'the other on its seat. y

8. A servo brake unit comprising a casing, a servo cylinder forming partof said casing, a disthe air enters the tributor valve housing attachedto said casing,

transmission mechanism mounted in said casing, pedal actuating means anda brake operating rod connected to said transmission mechanism in suchmanner as to provide a direct connection from the one to the other, alever connecting said transmission mechanism with a two part piston inthe said servo cylinder, linkage connecting said transmission mechanismwith a double acting valve in said distributor valve housing and bamemeans in said casing to prevent ingress of dust'to said distributorvalve housing.

9. A servo brake unit comprising a casing, a servo cylinder forming partof said casing, a distributor valve housing attached to said casing. a

cup washer, linkage connecting said transmission mechanismv with adouble acting valve disposed in said'distributor valve housing andcontrolling ports in the servo cylinder, an air inlet to the upper partof said casing and baille means adjacent said inlet and within saidcasing to prevent ingress of d t to said distributor valve housing.

10. A monobloc servo brake unit comprising a casing, a distributor valveand a servo cylinder mounted in said casing, a pedal actuated operatingrod extending into said casing, a brake operating rod extending intosaid casing in a position opposite to said pedal actuated rod, areaction lever mounted in said casing, a lost motion connection betweensaid an element carried by said reaction lever, a direct connectionbetween said element and said brake operating rod, a lost motionconnection between one `end of said reaction lever and a ,fixed pivot, aconnection between said one end oi' said reaction lever and saiddistributor valve, and a connection between the-opposite end ofsaidlever and a piston in said servo cylinder.

11. A monobloc servo brake unit comprising a casing, transmissionmechanism, and a servo cylinder all mounted in said casing, a reactionlever forming part of said transmission mechanism, a pedal actuatedoperating rod, a brake actuating rod, a bushing mounted in the saidreaction lever, a connection between the pedal actuated rod and saidbushing, pivot to /which the reaction lever is also loosely connected, apin carried by said br ke levers and extending through said bushing? andconnections between the ends of said n and the brake actuating rod.

' 12. A' monobloc servo casing. transmission mechanism.. and a servocylinder all mounted in said casing, a reaction lever forming part of apedal actuated operating rod, a brake actuatingv rod, .a bushing mountedin the saidreaction lever, a connection between the pedal actuated rodand said bushing, brake levers mounted over a iixed pivot to which thereaction lever is also loosely connected, a pin carried by said brakelevers and extending through said bushing, connections between the endsof said pin and the brake actuating rod. a pivotal connection betweenthe lower ends of the brake levers and the reaction lever and aconnection between the lower end of the reaction lever and the piston inthe servo cylinder.

13. In a servo actuated brake, ahousing, a

pedal actuated rod and brake levers mounted over a ixed4 brakel unitcomprising a said transmission mechanism,"

' entrain dust partici pair oi' spaced p otal movement about a andadapted to to a servomotor, 5 spaced parallel rod in closely adjacentcross me to said arms, a

arms in spaced paralle axis and said rod, an actu for endwisereciprocation one wall of said cross member midway and levers, so as toap thereto free from when it is recipr ber substantially axially atingelement and cation in an oppos means for connecting s ber to spacedregions o th respect to the g element to said eliminating any or saidbrake operating metrically'located wi connection of said actuatin crossmember, thereby actuating element -of said have their free i s 5'araliel arms iournalled for piviixed axis in said housing ends connecteda rod connected to said arms in relationship to said fixed axis, aA pairof parallel spaced levers iournailed on said twisting or ocated, a

aligned symmetrical relationship ber connected to said l relationship tosaid ilxed ating element mounted through an opening in housing'andconnected to said between said pairs of arms ply a turning movementaxial components brake operating memwith said actumounted for endwisereciproite wall o! said housing. and

aid brake operating memf said cross member symregion or tendency memberto set up twisting forces in said arms or levers.

14. The brake mechanism defined in claim 13,

wherein said levers a re disposed intermediate i said arms and'saidactuating element is connected to said cross member intermediate saidlevers. mechanism denned in claim 13,

15. The brake I wherein said brake oper ber outwardly of said arms.

1B. The brake wherein said actuating are connected to between.

17. In a brake a otally mounted @ing in one wall mechanism element atingmember is provided v with a forked end connected to said cross memdenedin 'claim 13,

and said levers a bushing surrounding said cross onship, so as to prooflost motion therectuating mechanism. a housing, a plurality of brakeactuating members pivin said housing, an air inlet openof said housingand an air outlet opening in another wall of said housing, saidactuatingmembers being disposed in the path of a valve mechanl operableto contr an air'inlet port opening in the path ing for preventing dustpa ried through said outlet o air iiow from said inlet to said escontained in the air stream,- to said housing andol brake actuation, andhaving communicating with the air housing, and a baille adjacent saidair outlet of air flow through said h ousrticles from being carpeninginto said valve of said housing outlet, so as to- SYDNEY EDGAR. wnurrr.STANLEY Howsan anon.

